It is shown according to ergonomic studies that, a visual field of human two eyes is a rectangle with an aspect ratio close to 16:9; and therefore, according to such aspect ratio, most of display devices (e.g., TV) in current market usually adopt a widescreen design, that is, a ratio of a number of pixels in a transverse direction to a number of pixels in a longitudinal directions is set to 16:9 for these display devices.
In the case that an aspect ratio of source image signal input to the display device is less than 16:9, for example, in the case that a digital TV standard definition signal having an aspect ratio of 4:3 is input, if it is needed to display the source image signal of 4:3 on the display device of 16:9 in full screen, the source image signal of 4:3 is required to be compressed in the longitudinal direction while no changes happen in the transverse direction, or the source image signal of 4:3 is stretched in the transverse direction while no changes happen in the longitudinal direction; that is, in the case that the source image signal of 4:3 is displayed in full screen in the above two manners, it is inevitable to deform the original image corresponding to the input source image signal. Accordingly, characters displayed by the display device are usually seemed undersized/overweight. If it is desired to keep the source image signal of 4:3 undeformed, a black portion with a certain width is required to be provided on left and right sides of the image on the display screen, which results in that the original larger-sized display device can only display a smaller-sized image.
Similarly, in the case that the aspect ratio of the source image signal input to the display device is greater than 16:9, for example, in the case that a recorded movie signal having an aspect ratio of 21:9 is input, if it is needed to display the source image signal of 21:9 on the display device of 16:9 in full screen, the movie signal of 21:9 is required to be greatly compressed in the transverse direction. That is, in the case that the movie signal is displayed in full screen in the above manner, it is inevitable to terribly deform the image. At present, in order to keep the image corresponding to the source image signal of 21:9 undeformed, the black portion is usually arranged on upper and lower sides of the image on the display screen, which also results in that the larger-sized display device can only display a smaller-sized image.
On such basis, for most of display devices (especially, TV) in current market, only in the case that the source image signal having an aspect ratio of 16:9 is input, people can see images without deformation in full screen. Since aspect ratios of current source image signals generally are 4:3 and 21:9, it is difficult to obtain a satisfying viewing experience in the case that the TV has the aspect ratio of 16:9.